**5. Conclusions**

The first part of the series illustrated how process engineering parameters for bioreactors used in the biopharmaceutical industry can be determined using CFD and how they can be validated. Furthermore, it was shown that CFD has become well established as a tool for characterising bioreactors, and that both hardware and software are constantly being improved to speed up the calculations and achieve higher accuracy. In this part of the series, practical application examples were used to demonstrate that with the appropriate choice of model, process engineering parameters can be determined to the required degree of accuracy (**Table 1**). This is independent of the mechanical drive for stirred, orbitally shaken, and wave-mixed bioreactor systems. Using different stirred bioreactors, it was possible to show that the calculated specific power input agrees with both the electrical and the torque measurement method. In addition, it was also demonstrated that the *k*L*a* value in a stirred system can be calculated in a way that takes coalescence and bubble breakup into consideration, and can be validated with the gassing-out method. Both the free surface and flow velocities in a wave-mixed system were determined using CFD and validated


#### **Table 1.**

*Overview of the investigated bioreactor systems with working volumes, solver used, turbulence models, number, and type of mesh cells as well as boundary conditions. The systems are divided into OpenFOAM and fluent cases according to the simulation software used.*

experimentally. In addition, the specific power input and the hydrodynamic stress were also determined for this system. Using the example of shake flasks, it was shown that the free surface can also be precisely determined for orbitally shaken systems, with the sickle height of the CFD and experimental validation differing by less than 2%. Furthermore, the influence of the contact angle on the specific power input was also examined. As shown in this series, CFD is used extensively for the characterisation of bioreactors and is likely to be used even more in the future.
